There are many processes for producing HFSI. However, none of the conventional processes are suitable for continuous production of HFSI. In many instances the conversion of HCSI to HFSI may be limited by equilibrium and that by selective removal of HCl the conversion could be shifted to the right. See, for example, a commonly assigned U.S. Pat. No. 8,722,005. However, typically a good conversion of HCSI to HFSI can be achieved using refluxing HF conditions and selective removal of HCl, which is not recovered in the condenser. While effective at achieving high conversion, this process requires a long reaction time and therefore a large reactor in commercial scale production. Large reactors for using hydrogen fluoride involve significant expense to ensure safe operation. Furthermore, the condenser that is used to recover HF from the HCl exhaust must operate a low temperature requiring refrigeration. Such refrigeration of the condenser adds to the overall cost of producing HFSI, thereby significantly limiting the commercial usefulness of this process.
Therefore, in order to achieve a significant commercial feasibility a process is needed that does not require a relatively long reaction time, a large reactor, and/or refrigeration of a condenser that is used in recovery of HF.